The collection of agro-meteorological data was initiated in 1985 and the network established consists of 84 stations and can be divided into four groups depending on the number of parameters measured:

64 "Class C" stations (termed "Climatological stations") where maximum and minimum temperature, dry and wet bulb temperature, and precipitation are measured and recorded once a day – at 9 o’clock a.m.

4 "special meteorological stations" which are located at the mountain passes. Apart from the parameters measured at the Class C stations, solar radiation and rainfall measured by an automatic rain gauge are recorded continuously.

4 snow gauging stations at the mountain pass.

12 "Class A" stations, which are the most, advanced type of stations has been installed covering whole of the country. Apart from the measurements at the "special meteorological stations, the following parameters are measured: wind speed, wind direction, soil temperature (at 5, 15 and 30 cm), and sunshine hours and pan evaporation.

The highest concentration of stations is found along or close to the main road from Thimphu to Trashigang, whereas there are very few stations in the northern part of the country.

The Hydrology Unit, Division of Power, Ministry of Trade & Industry is collecting hydrological and sediment data from various gauging stations in the country. The river gauging stations were upgraded during 1990-1991, as a part of the Bhutan Power System Master Plan Project for development of hydropower projects. Modern bank operated cableway, electronic water level recorder, loggers, etc were installed at the stations.

Presently the hydrological network in Bhutan consists of

13 Primary or Principal Gauging Stations (the new stations established during 1990-1991) and

8 Secondary Stations (the old stations which were established from early to late 1980s).

The Stations are spread over the country to provide a fairly good coverage of the 4 major river basins.

At the Principal stations, water levels are measured with automatic water-level recorders and data are stored in loggers at 15 minutes interval (now all became defunct due to some problems with pressure transducers and spare parts). However, manual readings of water level from wooden staff gauges are done twice a day at 9 am. and 3 p.m. Flow measurements are taken once a week with modern propeller current meters in order to establish and – if necessary – update the rating curve which is used to estimate the discharge (flow) from the recorded water level. At the secondary stations traditional float methods are used for discharge measurements resulting in less accurate discharge measurements than at the principal stations.

The hydrological data are mailed to the central office (Hydrology Section) in Thimphu at the end of every month. After conducting a screening exercise the data is fed in the computer software program called HYDATA, developed by Institute of Hydrology (now called Centre for Ecology & Hydrology, CEH) Wallingford, UK. Today the hydrology section maintains data from various rivers/streams ranging 10 to 11 complete years of processed data stored in the computer. Back up files in the form of hard copies, floppy diskettes, Zip disk, CD are maintained. The quality of the data is generally very good and the stations are also well maintained, although a few station are not working properly at the moment, due to damage equipment from flash floods.

Thus, so far the data from the hydrological network has been mainly used for the purpose of planning and design of hydropower projects, where particular hydrological analysis have been carried out in relation to these projects. However, data are also used by other sectors of the Government and NGOs. Hydrological data in Bhutan comprise only of river discharge and on more or less experimental basis, the suspended sediment data are collected presently from five station and has been planned to expand more in the future.